Method of inhibiting corrosion with aminomethylphosphonic acid compositions



United States Patent US. Cl. 2s2 3s9 18 Claims ABSTRACT OF THE DISCLOSURE Amiuomethylphosphonic acid compounds and soluble salts thereof, alone or in combination with zinc, dichromate, certain thiols and 1,2,3-triazoles and mixtures thereof, are disclosed as inhibiting the corrosion of metals by oxygen bearing waters.

This invention is a continuation-in-part of our copending application Ser. No. 534,947, filed Jan. 24, 1966, and now abandoned.

This invention relates to the use of aminomethylphosphonic acid compounds and salts thereof for inhibiting the corrosion of metals by oxygen-bearing waters. It also relates to aminomethylphosphonic acid compositions containing zinc, dichromate, certain thiols and 1,2,3-triazoles, and mixtures thereof and to corrosion inhibition therewith.

Oxygen corrosion is, of course, a serious problem in any metal-containing water system. The corrosion of iron and steel is of principal concern because of their extensive use in many types of water systems. Copper and its alloys, aluminum and its alloys, and galvanized steel are also used in Water systems and are subject to corrosion. We have discovered novel corrosion inhibitors which will inhibit oxygen corrosion in water systems Containing such metals.

We have found that aminomethylphosphonic acid compounds and soluble salts thereof (hereinafter referred to as the phosphonates) make effective corrosion inhibitors. These phosphonates include aminomethylphosphonic acid, amino bis (methylphosphonic acid), amino tris (methylphosphonic acid), compounds containing the above amino forms, and salts of any of the above acids. Such com pounds include compounds of the general formula:

(See US. Patents 2,599,807 and 2,609,390) where Alk is any alkylene carbon group (C H containing 2 to 6 carbon atoms, each R may be H, -CH COOM, or

I? CH2Il-OM M is H or a cation forming a water-soluble salt and n'=0 to 14 provided, however, that where n=0 at least one of the radicals represented by R are Patented Dec. 9, 1969 and where n is greater than zero at least /2 of the radicals represented by R are Ethylene diamine tetrakis (methylphosphonic acid) and itswater-soluble salts are preferred; amino tris (methylphosphonic acid) and its Water-soluble salts are also preferred compositions. Of the monoamines containing. only one or two methylphosphonate groups, we prefer the primary and secondary amines containing no other groups, i.e., those of the formula H N OH I (OM) 2 and EN loHzi wMhh although we may also use substituted amines, such as, for example, diethanol amino (methyl phosphonates). Lower alkanol substituted monoamines having at least one methyl phosphonate group are contemplated in our invention. We have also successfully used compounds over the range 11:0 to 14, including as representative compounds nitrilotris (methylphosphonic acid) in which 11:0; ethylenediamine tetrakis (methyl phosphonic acid) in which n=l; diethylenetriamine pentakis (methyl phosphonic acid) in which m=2; pentamethylenehexamine octakis (methylphosphonic acid) in which 11:5; and polyethyleneimine polykis (methylphosphonic acid) in which n=l4.

We have performed numerous experiments which demonstate the effectiveness of those phosphonates in inhibiting metallic corrosion. In these experiments 1%" x 1%" No. 1010 AISI steel coupons were weighed and placed in beakers containing 1000 ml. water at 35 C. and various amounts of corrosion inhibitor. The water contained 11 p.p.m. bicarbonate, 18 p.p.m. chloride, 78 p.p.m. sulfate, 20 p.p.m. calcium, and 6 p.p.m. magnesium, and had a total hardness as CaCO of 76 p.p.m. The coupons were gently agitated for five days, after which they were removed, cleaned, and reweighed. The amount of corrosion that had taken place was determined by the loss in weight and expressed in terms of milligrams of steel consumed per square decimeter of surface per day (m.d.d.). Results of tests with severalv phosphonates are given in Table I.

TABLE I.INHIBITION OF CORROSION OF STEEL WITH AMINO METHYL PHOSPHONATES Ethylenedia- Amino tris mine tetrakis Disodium (methyl phos- (methyl phosdiethanolamino Inhibitor Cone, phonic acid), phonic acid), methylphosp.p.m. m.d.d. m.d.d. phonate, m.d.d.

Our phosphonates will inhibit corrosion of ferrous metals when maintained in a water system at a concentration of at least about 20 p.p.m., and preferably about 50 p.p.m.; maximum concentrations are determined by economics. Because they attack copper to some degree, use of the phosphonates by themselves is recommended only in water systems which do not contain copper.

As with all concentration ranges given throughout this patent, the concentrations of inhibitor needed to inhibit corrosion effectively will depend on the characteristics of the water system being treated and the particular phosphonates used. The ranges given are a general indication 3 4- of the concentrations needed; exact concentrations must experiments similar to those already described and show be determined by examination of the water system to be the synergism between the amino phosphates and chromate treated. or dichromate.

We have discovered a synergistic effect on corrosion Tables V, VI, and VII each use different amino phosinhibition between phosphonates and the zinc ion; that is, phonate compounds; Table V illustrates results with the use of the phosphonates with the zinc ion more eifec- 5 total inhibitor mixtures of 10 and 20 parts per million, tively inhibits corrosion than does an equal concentration Table VI illustrates results at 50 parts per million total inof either the phosphonate or the ZlIlC ion alone. Experihibitor mixture, and Table VII employs an inhibitor mixments to show the synergism between the phosphonates ture at 10 parts per million. and were Performed the Same mafmer as those 10 TABLE V.INI-IIBI'IION OF CORROSION OF STEEL WITH previously described for Table I. Table II gives the results SODIUM DICIIROMATE-AMINO TRIS (METHYLPIIOS- of these experiments. The zinc ion was introduced as zinc PHONIC ACID) MIXTURES sulfate. In all tables, the heading (m.d.d.) means mg] l35C-PH 65] Square dec1m6ter/daY- Inhibiting Composition, Wt. percent TABLE II.-INHIBITION OF CORROSION or STEEL WITH 15 Amino Tris W ZINC ION AND AMINO TRIS (METHYLPHOSPHONIC ACID) (Methylphosphonic Acid) 0 10 p.p.m. 20 p.p.m.

Inhibitor Composition Wt. Percent 8 3 g Corrosion Rate (m.d.d.) 40 8 5 Amino lll'lS 6O 7 2 7 4 (methylene phos- 10 50 0 g 8 phonic acid) Zinc p.p.m. p.p.m. p.p.m. p.p.m. p.p.m 100 s0 69 3s 14 0.9 1.4 TABLE VI.-INHIBITION OF CORROSION OF STEEL WITH 60 42 1.3 1.2 0.8 0.6 SODIUM DICHROMAIE-DISODIUM DIE'IHANOLAMINO 3g 3g %.g 231) METHYL PHOSPHATE 0 117 1'10 34 a: s 31 2 25 P 1 Disodium Diethaiiolamino Na2CrzO1 Weight Lossat Similar experiments with other phosphonates were also Methy lwspiionate (W gh 50 D-p- Inhlbl (Weight percent) percent) tor Level (in.d.d.)

performed. Tables III and IV show large decreases in corrosion when small amounts of zinc were present with 8 A ethylenediamine tetrakis (methylphosphonic acid) and 30 60 7.'7 with disodium diethanolamine methyl phosphonate. g8

TABLE III 100 5.2

Influence of zinc (sulfate) on inhibition of corrosion of BLE Vin-INHIBITION 0F CORROSION F STEEL WITH acid) (10 p.p.m.)

. E (thylenediamiue Tetrakis Zn++ (p.p.m.) Corrosion rate (m.d.d.) (Methylphosphonic Acid) Naiori01 Weight Loss 0 Wt. percent) (Wt. percent) (m.rl.d) 0 108 2 20 0. 2 4 s Corrosion in most water systems may be inhibited by TABLE IV adding about 1 to 100 p.p.m. amino phosphonate and 49 about 1 to 100 p.p.m. chromate or dichromate; preferably about 5 to 25 p.p.m. amino phosphonate and about pp m.) 5 to 25 p.p.m. chromate or dichromate is added.

We have also found that compositions of amino phos- Zn++ (P-P- COITOSiOIl fate phonates, zinc iron, and chromate or dichromate are useful in inhibiting the corrosion of metals. The inhibiting action of zinc and dichromate compositions has been shown in Hatch US. Patent 3,022,133; thus, all three components of this composition are mutually synergistic. The co-action of zinc and dichromate illustrated in US. Patent 3,022,133 remains unaffected by the presence of amino phosphonates and the other ingredients of our in- Influence of zinc ion on inhibition of corrosion of steel with disodium diethanolamine methyl phosphonate (50 f g g s g to 100 in 5%: hibitors mentioned herein. Tables VIII and IX give the p p a t zlmf: londwl m I resuls of experiments conducted as previously described iorroslon mos W3 er sys t 8 pre erre come using these corrosion inhibiting compositions. tion range is about 5 to 25 p.p.m. phosphonate and about 5 to 25 p p In zinc io TABLE VIIL-INHIBITION OF CORROSION OF STEEL WITH AMINO TRIS (METHYLPHOSPIIONIC ACID)SODIUM Amino phosphonate and a zinc salt may be mixed as a DICHROMAlE-ZINC (SULFATE) MIXTURES dry composition can be fed into a Water system. Such [pH=8] a composition having maximum synergism between the amino phosphonate and the zinc ion comprises about 10% to soluble zinc salt and about 20% to amino Amino Tris Methyl- SOdium Zinc++ gg g Concentration (p.p.m.)

phosphonate; preferably it comprises about 20% to 60% phosphome Acid Dmhiomate soluble zinc salt and about 40% to 80% amino phospho- 1 g 1 g 2 nate. 2.5 2.5 216 We have also found synergism between the amino phos- 2 g phonates and chromate or dichromate. Because chromate ,25 15 and dichromate are each readily converted into the other 3-2 by a change in pH, it is understood that both will be 5: 515 2: simultaneously present at most pHs even though only one 5 '2 -2 is mentioned, Tables V, VI, and VII give the results of 75 TABLE IX.-INHIBITION OF CORROSION OF STEEL WITH ETHYLENEDIAMINE TETRAKIS (METHYLPHOSPHONIC %%I1]3I%-SSODIUM DICHROMATE-ZINC (SULFATE) MIX- TABLE XIV.-INFLUENCE OF ZINC (SULFATE) ON COR- ROSION OF COPPER IN PRESENCE OF 50 P.P.M. DIETH- ZIIEgETRIAMINE PENTAKIS (METHYL PHOSPHONIC [p l [pH=7.0]

Concentration (p .p.m.) 5 Zinc Cone.

Ethylenediamine 'Ietrakis Sodium Weight Loss Percent of Wt. Loss (Methylphosphonic Acid Dichromate Zinc++ (m.d.d.) P.p.m D'IPMP Cone. (m.d.d.)

TABLE X.-INHIBITION OF CORROSION OF STEEL WITH DIETHYLENETRIAMINE PENTAKIS (METHYL PHOS- PHONIC ACID) ALONE AND IN THE PRESENCE OF ZINC (SULFATE) Wt. Loss (m.d.d.)

With Zinc (30% of Alone DTPMP Cone.)

DTPMP Cone. (p.p.m.)

Wt. Loss (m.d.d.)

Plus Zn (30% of the Phosphonic PMHOMP Cone. (p.p.m.) Alone TABLE XV.INFLUENCE OF ZINC (SULFATE) ON COR- ROSION OF ARSENICAL ADMIRALTY BRASS IN PRES- ENCE OF 50 P.P.M. NITRILOTRIS (METHYL PHOSPHONIC ACID) [pH 6 91 Zinc Cone.

Wt. Loss (m.d.d.)

Zinc Cone.

Percent of DTPMP Cone.

Wt. Loss (m.d.d.)

TABLE XVII-EFFECT OF pH ON CORROSION OF COPPER IN PRESENCE OF 50 P.P.M. DIETHYLENETRIAMINE PENTAKIS (METHYL PHOSPHONIC ACID) AND INFLU- ENCE THEREON OF 15 P.P.M. ZINC Wt. Loss (m.d.d.)

TABLE XII-INHIBITION OF CORROSION OF STEEL WITH POLYETHYLENEIMINE POLYKIS (METHYL PHOS- PHONIC ACID) ALONE AND IN THE PRESENCE OF ZINC (SULFATE) TABLE XIII.-INFLUENCE OF ZINC (SULFATE) ON COR- ROSION OF COPPER IN PRESENCE OF 50 P.P.M. NITRI- LOTRIS (METHYL PHOSPHONIC ACID) Percent of NTMP Cone.

Zinc Cone. (p.p.m.) Wt. Loss (m.d.(l)

ore-unopocoooo Alone With Zinc We have found that the amino phosphonate inhibitors are effective over a rather wide pH range although below a pH of about 3 their inhibitive action decreases considerably. If the pH of the water being treated is too low, it may be necessary to raise it by the addition of alkali in order to achieve eiIective corrosion inhibition. Generally, slightly lesser amounts of corrosion inhibitor are needed for effective inhibition at higher pH levels. Best results are obtained at a pH between about 5 and about 9.

Table XIII shows the influence of zinc on the corrosion of copper in the presence of nitrilotris (methyl phosphonic acid). Table XIV contains similar data for diethylenetriamine pentakis (methyl phosphonic acid). The addition of zinc causes a pronounced decrease in the attack on copper in each case. Between 30 and 40% zinc is required with nitrilotris (methyl phosphonic acid), While somewhat less (i.e., 20 to 30% zinc) suffices with diethylenetriamine pentakis (methyl phosphonic acid).

Zinc exerts a similar inhibitive action on the corrosion of arsenical admiralty brass in the presence of these aminomethyl phosphonates. This is illustrated by the data for nitrilotris (methyl phosphonic acid) in Table XIV and those for diethylenetriamine pentakis (methyl phosphonic acid) in Table XVI. Again, a somewhat greater quantity of zinc is required for the nitrilotris (methyl phosphonic acid) than for the diethylenetriamine pentakis (methyl phosphonic acid).

The range of pH over which zinc provides adequate protection of copper and its alloys in solutions of these aminomethyl phosphonic acid compounds is rather restricted. This is illustrated by the data in Table XVII Which shows the influence of pH on the corrosion of copper in the presence of 50 p.p.m. diethylenetriamine pentakis (methyl phosphonic acid) plus 15 p.p.m. zinc. Adequate protection is not attained when the pH drops much below 7.

The inclusion of a 1,2,3-triazole or a thiol of a thiazone, oxazole or imidazole will afford greater protection of copper and its alloys over a considerably expanded pH range. Two p.p.m. 2-mercaptobenzothiazole sutficed to reduce the attack of copper in solutions of 50 p.p.m. of either nitrilotris (methyl phosphonic acid) or diethylenetriamine pentakis (methyl phosphonic acid) containing 15 p.p.m. zinc to a level such that no detractable weight loss was observed at pH values as low as 4.

These copper inhibitors are also effective for prevention of attack on copper and its alloys by high levels of these aminomethylene phosphonates. Five p.p.m. Z-mercaptobenzotriazole sufiiced to prevent detectable weight loss of copper strips or pickup of copper in 2000 p.p.m. diethylenetriamine pentakis (methyl phosphonic acid) over the pH range of 3 to 8.

Concentrated solutions of chromate and amino phosphonate should be avoided because at high concentrations chromate or dichromate will tend to oxidize the phosphonates and thereby render them ineffective. Thus, when a corrosion inhibitor which employs both chromate and amino phosphonate is used, the chromate and amino phosphonate should be fed separately into the Water system.

We have found that the inclusion in an amino phosphonate corrosion inhibitor of 1,2,3-triazoles or a thiol of a thiazole, an oxazole, or an imidazole as described respectively in Hatch US. Patents 2,941,953 and 2,742,369 (hereinafter referred to as thiols and 1,2,3-triazoles) will inhibit the phosphonate attack on copper. This composition makes a phosphonate corrosion inhibitor useful in an iron or steel water system containing copper; zinc ion may also be present in the inhibitor. The preferred 1,2,3- triazole is 1,2,3-benzotriazole of the formula The preferred thiols of a thiazole, an oxazole, or an imidazole are 2-mercaptothioazole Z-mercaptobenzoxazole and 2-mercaptobenzimidazole Tables X and XI give the results of experiments performed as previously described and show that the amino phosphonates and water-soluble 1,2,3-tn'azoles or a thiol of a thiazole will inhibit the corrosion of copper.

TABLE XVIII Influence of 1,2,3-benzotriazole on corrosion of copper in water treated with 100 p.p.m. amino tris (methylphosphonic acid) pH 8 1,2,3-benzotriazole Weight loss concentration (p.p.m.) (m.d.d.) 0 8.6 0.1 0.07

TABLE XIX Influence of Z-mercaptobenzothiazole on corrosion of copper in water treated with 100 p.p.m. amino tris (methylphosphonic acid) pH=8 2-mercaptobenzothiazole Weight loss concentration (p.p.m.) (m.d.d.

Where the water system containing copper is an open or once through system about 3 to 100 p.p.m. amino phosphonate, about 0.05 to 5 p.p.m. thiol or 1,2,3-triazole, and up to about 100 p.p.m. zinc ion are generally satisfactory concentrations; preferably the concentrations are about 5 to 25 p.p.m. amino phosphonate, about 0.5 to 2 p.p.m. triazole or thiol, and about 5 to 25 p.p.m. zinc lOIl.

A dry composition may be made which may be fed into the Water system containing copper. Such a composition would consist of about 20% to 90% amino phosphonate, about 1% to 10% thiol or 1,2,3-triazole, and up to about 79% soluble zinc salt; preferably, it would consist of about 38% to 90% amino phosphonate, about 2% to 10% thiol or 1,2,3-triazole, and up to about 60% soluble zinc salt.

It should be noted that the corrosion inhibitors of this invention may be used in conjunction with various Well-known inhibitors such as the molecularly dehydrated phosphates.

Thus, it may be seen that this invention relates to amino methylphosphonic acid compounds and salts thereof as corrosion inhibitors. We do not intend to be limited to any compounds, composition, or methods disclosed herein for illustrative purposes. Our invention may be otherwise practiced and embodied within the scope of the following claims.

We claim:

1. A composition useful for inhibiting the corrosion of metals in a water system consisting essentially of about 10% to 80% of a water soluble Zinc salt and about 20% to of a compound of the general formula where Alk is any alkylene carbon group containing 2 to 6 carbon atoms, R may be a member selected from the group consisting of H, CH COOM and -CH2-i:-OM

M is a member selected from the group consisting of H and a cation forming a water soluble salt, n=-14 provided, however, that where n=0 at least one of the radicals represented by R is ll CH POM and where n is greater than zero at least /2 of the radicals represented by R are 2. The composition of claim 1 wherein said compound is selected from the group consisting of ethylenediamine tetrakis (methylphosphonic acid) and Water soluble salts thereof.

3. The composition of claim 1 wherein said compound is selected from the group consisting of amino tris (methylphosphonic acid) and Water soluble salts thereof.

4. Composition of claim 1 wherein said zinc compound is Zinc sulfate.

5. A composition useful for inhibiting the corrosion of metals in a water system which contains cuprous metals consisting essentially of:

(a) about to 90% of a compound of the general formula N(A1k-N)..R R l where Alk is any alkylene carbon group containing 2 to 6 carbon atoms, R may be a member selected from the group consisting of H,

M is a member selected from the group consisting of H and a cation forming a water soluble salt, n=0l4 provided, however, that where n=0 at least one of the radicals represented by R is and where w is greater than zero at least A: of the radicals represented by R are 10 phosphonic acid of (a) is amino tris (methylphosphonic acid).

9. A method of inhibiting the corrosion of non-cuprous metals in a water system comprising maintaining in the water of said system at least about 20 ppm. of a compound of the general formula N-(Alk-Nh-R R l where Alk is any alkylene carbon group containing 2 to 6 carbon atoms, R may be a member selected from the group consisting of H, CH COOM and M is a member selected from the group consisting of H and a cation forming a water soluble salt, n=0-14 provided, however, that where n=0 at least one of the radicals represented by R is and where n is greater than zero at least /2 of the radicals represented by R are 10. The method of claim 9 wherein said compound is selected from the group consisting of ethylenediamine tetrakis (methylphosphonic acid) and water soluble salts thereof.

11. The method of claim 9 wherein said compound is selected from the group consisting of amino tris (methylphosphonic acid) and water soluble salts thereof.

12. A method of inhibiting the corrosion of ferrous metals in a water system comprising maintaining in the water of said system about 2 to p.p.m. zinc ion derived from water soluble zinc salts and about 3 to 100 ppm. of a compound of the general formula where Alk is any alkylene carbon group containing 2 to 6 carbon atoms, R may be a member selected from the group consisting of H, CH COOM and oH2-i oM,

M is a member selected from the group consisting of H and a cation forming a water soluble salt, n=O-14 provided, however, that where n=0 at least one of the radicals represented by R is and where n is greater than zero at least /2 of the radicals represented by R are 13. The method of claim 12 wherein said compound is selected from the group consisting of ethylenediamine tetrakis (methylphosphonic acid) and soluble salts thereof.

14. The method of claim 12 wherein said compound is selected from the group consisting of amino tris (methylphosphonic acid) and soluble salts thereof.

15. A method of inhibiting the corrosion of metal in a water system comprising maintaining in the Water of said system:

(a) about 1 to 100 p.p.m. of a compound of the general formula where Alk is any alkylene carbon group containing 2 to 6 carbon atoms, R may be a member selected from the group consisting of H, --CH COOM and -CHz] OM,

M is a member selected from the group consisting of H and a cation forming a water soluble salt, n=-l4 provided, however, that where n=0 at least one of the radicals represented by R is and where n is greater than zero at least /2 of the radicals represented by R are where Alk is any alkylene carbon group containing 2 to 6 carbon atoms, R may be a member selected from the group consisting of H, CH COOM and II CHz-POM,

M is a member selected from the group consisting of H and a cation forming a water soluble salt, n=0-14 provided, however, that where n=0 at least one of the radicals represented by R is and where n is greater than zero at least /2 of the radicals represented by R are (b) about 0.05 to 5 p.p.m. of a compound selected from the group consisting of 1,2,3-triazoles, thiols of thiazoles, thiols of oxazoles, and thiols of imidazoles, and

(c) up to about 100 p.p.m. zinc ion derived from water soluble zinc salts.

17. A method of inhibiting metal corrosion in closed recirculating water systems containing cuprous metals comprising maintaining in the water of said system:

(a) about 500 to 5,000 p.p.m. of a compound selected from the group consisting of amino methylphosphonic acids and water soluble salts thereof, and

(b) about 0.1 to 10 p.p.m. of a compound selected from the group consisting of 1,2,3-triazoles, thiols of thiazoles, thiols of oxazoles, and thiols of imidazoles.

18. The composition of claim 1 wherein said compound is selected from the group consisting of ethylenetriamine tetrakis (methylphosphonic acid) and water soluble salts thereof.

References Cited UNITED STATES PATENTS 2,337,856 12/1943 Rice et al. 252-387 X 2,742,369 4/1956 Hatch 252389 X 3,022,133 2/1962 Hatch 21-2.7 3,316,331 4/1967 Sims 252389 X 3,336,221 8/1967 Ralston 252-8.55 X 3,346,488 10/1967 Lyons et al. 252- OTHER REFERENCES Monsanto Chemical Co., Sodium Phosphates for Industry, 1959, pp. 14, 15, 16, 22, 23.

LEON D. ROSDOL, Primary Examiner I. GLUCK, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,483,133 December 9 1969 George B. Hatch et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 33, "those" should read these Column 3, line 63, after "composition" insert which Column 4, TABLE VI, in the heading, line 3thereof, "PHOSPHATE" should read PHOSPHONATE TABLE VII, in the heading to the first column, line 1 thereof, "E(thylenediamiue" should read (Ethylenediamine same table, in the heading to the first column, line 3 thereof, "Wt. percent)" should read (Wt. percent) same column 4, line 47, "5" should'read 2 line 49, "iron" should read ion line 58, "resuls" should read results Column 7, line 15, "thiazone" should read thiazole Signed and sealed this 3rd day of November 1970.

(SEAL) Attest:

EDWARD M.FLETCHER',JR,. WILLIAM E. SCHUYLER, JR. Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,483,133 December 9, 1969 George B. Hatch et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 33, "those" should read these Column 3, line 63, after "composition" insert which Column 4 TABLE VI in the heading, line 3 thereof, "PHOSPHATE should rea PHOSPHONATE TABLE VII in the heading to the first column line 1 thereof, "E(thylenediamiue" should read (Ethylenediamil same table in the heading to the' first column, line 3 there( "Wt. percent)" should read (Wt percent) same column 4 line 47, "5" should read 2 line 49 "iron" should read ion line 58 "resuls" should read results Column 7 line 15, "thiazone" should read thiazole Signed and sealed this 3rd day of November 1970 (SEAL) Attest:

EDWARD M.FLETCHER,JR. I WILLIAM E SCHUYLER, JR. Attesting Officer Commissioner of Patents 

